1. Field of the Invention (Technical Field)
Embodiments of the present invention relate to a transesterification process that extracts oils from an algal biomass. Embodiments of the present invention also relate to a method and system for the direct liquefaction and conversion of wet algal biomass into biodiesel via a single-step supercritical alcohol process.
2. Description of Related Art
Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
Microalgae, a third generation biofuel resource, has the potential to become a viable feedstock due to their high oil content and environmental-friendly nature. The major challenge, however, has been the high cost of recovering the oil from the microalgae prior to converting it into biodiesel. While there are many extraction methods such as solvent extraction, supercritical fluid extraction, ultrasonic extraction, and mechanical pressing; they require longer extraction times, large volumes of solvents, and are energy- and cost-intensive. Unlike vegetable oils from various crops that can be extracted by crushing the oil seeds followed by a solvent extraction, releasing oil from algal cells is hindered by a rigid cell wall structure. Thus, mechanical crushing seems to be an ineffective way to extract the oils from the algal biomass. In addition, using solvents for extraction may involve an expensive separation process. Microwave-assisted extraction or extractive transesterification is an alternative to address the above concerns as the ability of the microwaves to penetrate through the cell wall structure which results in an efficient recovery of oils and lipids.
Microwave irradiation has been used in the past to extract the oils from biomass, soils and vegetable feedstock. In microwave-assisted extraction, rapid generation of heat and pressure within a biological system forces out compounds from a biological matrix, producing good quality extracts with better target compound recovery. The rapid heating leads to localized high temperature and pressure gradients which assist in cellular wall degradation and enhanced mass transfer rates.
A process which provides simultaneous oil extraction and transesterification is worthwhile to develop. Aresta et al. conducted thermochemical liquefaction using wet algal biomass and supercritical CO2 extraction using dry algal biomass. Both of the processes seem to be energy intensive by the reaction conditions they reported (thermochemical liquefaction conditions: 250-395° C. for 1 hour and supercritical CO2 extraction conditions: 50° C., 2.60 MPa for 7 hours). A recent study has demonstrated the simultaneous extraction and transesterification (in-situ tranesterification) of the wet algal biomass in supercritical methanol conditions. In a microwave-assisted extraction and transesterification process, as it has been demonstrated in many organic and biodiesel synthesis studies, it is anticipated that the reaction can be conducted at atmospheric pressures and temperatures merely close to the boiling point of methanol with much shorter reaction time.
Biodiesel can also be produced from algal biomass and oils by extraction-transesterification, direct methanolysis and transesterification methods. Traditionally, algal biodiesel has been produced from wet algal biomass in a series of steps including preparation of dry algae powder, extraction of algal oils with chemical solvents, and conversion of the algal oil to biodiesel with a catalyst. Drying the biomass and extraction of algal oils by conventional methods are both energy and cost-intensive. An alternative to the conventional extraction and transesterification methods is supercritical process. Using water in wet algae as a tunable co-solvent in supercritical methanol process not only accelerates the conversion of fats and algal oils to fatty acid methyl esters (FAMEs), but also increases solubility and acidity.
There is a present need for a single-step supercritical process for simultaneous extraction and transesterification of wet algal biomass such that FAMEs can be produced from polar phospholipids, free fatty acids, and triglycerides by increasing fluidity and volatility while reducing the polarity of the high-energy molecules in algae at supercritical conditions. There is further a need for a supercritical process are that operates at modest temperatures and has a lower energy requirement compared to conventional extraction and transesterification methods.
Objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.